linux-ext4 - Re: [PATCH 04/26] jbd2: Refine waiting for shadow buffers

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Message-ID: <20130604160929.GE25160@thunk.org>
Date:	Tue, 4 Jun 2013 12:09:29 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 04/26] jbd2: Refine waiting for shadow buffers

On Fri, May 31, 2013 at 11:42:37AM +0200, Jan Kara wrote:
> Currently when we add a buffer to a transaction, we wait until the
> buffer is removed from BJ_Shadow list (so that we prevent any changes to
> the buffer that is just written to the journal). This can take
> unnecessarily long as a lot happens between the time the buffer is
> submitted to the journal and the time when we remove the buffer from
> BJ_Shadow list (e.g.  we wait for all data buffers in the transaction,
> we issue a cache flush etc.). Also this creates a dependency of
> do_get_write_access() on transaction commit (namely waiting for data IO
> to complete) which we want to avoid when implementing transaction
> reservation.
> 
> So we modify commit code to set new BH_Shadow flag when temporary
> shadowing buffer is created and we clear that flag once IO on that
> buffer is complete. This allows do_get_write_access() to wait only for
> BH_Shadow bit and thus removes the dependency on data IO completion.
> 
> Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

Applied, thanks.

						- Ted
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